websockets

WebSockets is a communication protocol that enables full-duplex, two-way communication over a single, long-lived TCP connection. It was designed to support real-time web applications by allowing both client and server to send messages independently, reducing the need for repeated HTTP requests and low-latency interactions. The protocol is defined in RFC 6455 and operates after an initial HTTP-based handshake that upgrades the connection to a persistent WebSocket.

The connection starts with a client using the ws:// or wss:// URI scheme (the latter secured with TLS). During the handshake, the client sends an HTTP/1.1 Upgrade request including headers such as Upgrade: websocket and Connection: Upgrade, along with a Sec-WebSocket-Key. The server replies with an HTTP 101 Switching Protocols response and a Sec-WebSocket-Accept value derived from the key. After the upgrade, the HTTP layer is no longer used for data frames; the connection remains open and both ends can send frames at any time.

Data transmission uses frames with simple message boundaries. Text frames carry UTF-8 text, while binary frames carry binary data. Control frames include ping, pong, and close. Data frames may be fragmented across multiple frames. Client-to-server frames must be masked, whereas server-to-client frames are not. Opcodes identify frame types, such as 0x1 for text and 0x2 for binary. Extensions like permessage-deflate can be negotiated to compress payloads.

Common use cases include chat, live dashboards, real-time collaboration, multiplayer games, and notification systems. WebSockets offer low latency and reduced overhead compared with long polling or frequent HTTP requests but require persistent connections, careful scaling, and appropriate security measures, including the use of TLS in wss and proper handling of authentication and subprotocols.